Printing ink containing alkyd resin and a mixed hydrocarbon solvent



Patented Feb. 13, 1951 PRINTING INK CONTAINING ALKYD RESIN AND A MIXEDHYDROCARBON SOLVENT Joseph G. Curado, Bergen County, N. J., assignor toSun Chemical Corporation, New York, N. Y.,

a corporation of Delaware No Drawing. Continuation of application SerialN0. 346,801, July 22, 1940.

This application March 19, 1946, Serial No. 655,593

3 Claims. (Cl. 26033.6)

This invention relates to printing inks of the type characteristicallycontaining a binder such as a resin or cellulose derivative, a solventthereof, and an insoluble pigment; also to the preparation andutilization of such inks.

In most of the present-da commercial printing operations, the attainmentof relatively high operating speeds is an important requirement. It hastherefore been necessary to prepare and use printing inks which set withsuflicient rapidity to prevent smearing, smudging or offsetting underpresent high-speed operating conditions. This is especially a problemwhere a considerable time element, compared to press speeds, wouldelapse before the ink sets sufficiently to prevent offsetting.

In high grade half-tone and multi-color printing, using so-called heatsetting inks, for example, printing inks suitable for this purpose arenow commonly made of resin, a vehicle or solvent for the resin, and aninsoluble pigment, as the principal ingredients. The resin and solventmixture is commonly referred to as the varnish. These inks acquire theirinitial set after print ing by evaporation of the solvent or bypenetration of both resin and solvent into the paper web, or by acombination of both. Final complete drying is attained, in either case,by evaporation, or removal from the imprinted ink of substantially allof the solvent, leaving more or less of the resin binding the pigmentparticles together and to the paper or other surface which has beenprinted.

When initial setting is brought about by penetration of the varnish intothe paper, as in the usual newspaper inks and newspaper printing, forexample, the pigment is relatively insecurely held, and smudges whenlightly rubbed, even when dry. This is not a great disadvantage withsome classes of printed products, but where greater durability andhigher grades of printing are required, it is particularly undesirable.

When the setting of the ink is brought about by evaporation of thesolvent, as for example with inks used in the printing of highlycalendered or coated stock for books and magazines i. e., so-called bookpaper, two difliculties are present. It is clear that the more volatilethe solvent is, the more rapid will be the setting of the ink, otherconditions being the same. However, a readily volatile solvent causesnot only drying of the ink on the press, with obvious resultingdifficulties, but also tends to cause a change in the physicalcharacteristics of any of the ink which is exposed to the atmosphereprior to application, due to loss of solvent, and hence change inviscosity and other properties.

In recent years higher printing speeds were demanded by the publishers,particularly in the field of letter press magazine printing with a viewto matching very high printing speeds long obtained in newspaperprinting and more recently through the use of highly volatile solventinks in intaglio printing. Because of the paper used in this magazineletter press field the required quality of work had caused the useofinks setting by evaporation or chemical action as opposed to very highspeed setting through penetration as in newspaper work. To meet thedemands for higher speeds in this field the press manufacturers promptlygave the required press speeds. It has long been known to useevaporators or driers in presses following the printing mechanism, toeffect initial or final set of the printed ink, and at the same timethat press speeds were increased evaporators or driers of increased heatinput capacity were used in the presses. As a result solvents could beused whose volatilty is such that there is no objectionable evaporationat the temperatures existing in the press room and at the ink fountainsand printing mechanism; and by sufliciently increased heat applicationto the printed paper after it leaves the printing mechanism thetemperatures may be raised sufficiently to cause rapid, or evensubstantially instantaneous, evaporation of the solvent. This heatingmay be suflicient to cause such set as will prevent smudging insubsequent handling and thus avoid the use of smudge or offset sheets,while giving high quality work at high press speeds. While various drierarrangements were tried the insistent demands of the printers for inkswhich would set almost instantaneously to permit extremely high pressspeeds in web perfecting presses for half-tone and multicolorreproductions rather promptly led to the adoption of greatly increasedheat input, direct flame driers; and the most widely used drier for thistype of work has become one using gas burners positioned closelyadjacent the travelling web to impinge high temperature flames directlyupon the printed surface of the paper. At the high speeds of web travelthe localized high temperature flames will heat the ink on the paperalmost instantaneously to evaporation without charring the paper itself.In some instances the burners are made with refractory parts whichbecome incandescent and assist in the high heat input, and the solventsordinarily available for such inks also are inflammable and the burningof the vaporized solvent may be beneficial and simplify the inherentproblem of evacuating vapors and fumes from about the presses whichmight otherwise be objectionable or deleterious to the health of theoperator. Practically all printing inks heretofore in use which relyessentially on solvent evaporation for setting represent a compromisebetween a high enough volatilty to insure adequate speed of setting anda low enough volatility to insure stability of the ink on the press.

When reference is made herein to drying or setting to non-offsettingcondition, this term should be understood in its usual sense in the artherein referred to. It is, of course, clear that the conditions whichefiect an offset of any given impression may be mild or severe. Forexample, almost any impression even of good quality will offset evenweeks or months after printing if subjected to sufificient pressure andrubbing action. However, under ordinary printing conditions, which arethose referred to herein, a printed impression is considered to benon-offsetting if it will not ofiset onto paper or other surfaces withwhich it comes in contact during the usual operations subsequent to theprinting operations, such as backing up, winding, folding, and stackmg.

One object of the invention is to provide an ink having binder insolution or suspension in a composite vehicle which is of such characterand in such proportion to the binder that minor changes in the ratio ofa component of the vehicle with respect to the binder will cause settingof the ink to non-offsetting condition.

Still another object is to provide such an ink in which the vehiclecomprises a component which is an inadequate solvent for the binder(such as a resin) and another component which is miscib.e with saidnon-solvent component and is an adequate solvent for the binder when inadmixture with the non-solvent component and in which these componentsare so proportioned in admixture that even minor reduction in the amountof the solvent component will cause setting of the ink to non-offsettingcondition.

Another object is to provide. such an ink in which the binder is a resinor the like which is in such proportion to the predetermined solventnonsolvent miscible components that predetermined reduction in minor amountof the solvent component will cause gelation of the binder tonon-offsetting condition.

Still another object of the present invention is to provide a printingink of the resin-solventinsoluble pigment type which can be set rapidlyto non-smearing, non-offsetting condition; preferably, but notnecessarily, with the aid of heat.

Another object is the preparation of such inks with the use of solventswhich are relatively nonvolatile at room and press temperatures.

Another object is to provide a printing ink which sets to non-smearing,non-offsetting condition without requiring the evaporation of a largeproportion of the solvent in the ink.

A further object is to provide a printing ink which begins its initialset so rapidly that, even if placed in offsetting relation with anothersurface before it has set, it will smudge and smear less than hithertoavailable inks of this general type. I

Also an object is to provide an ink comprisin a binder and a solvent-nonsolvent vehicle in a. system having a critical gelation point orbalance, with the system approaching but short of the gelation point bya predetermined amount so that minor disturbance of the system byvariation of such ratio, as by decrease of a minor fraction of thesolvent component will cause such disturbance in the systemthat agelation will occur.

Another object is to provide such an ink having such solvent-binderratio that modification of the ratio of solvent to binder by an amountsubstantially equal to that which would occur in substantially oneminute when the ink is imprinted on a coated book paper will cause theink in the imprint to set to non-ofisettingcondition.

Still another object is to provide a printing ink which Will set in thecold relatively quickly as compared with ordinary drying-oil inks, andeven withother known volatile-solvent heat drying inks, thus permittingcold (room temperature) printing and drying, if desired-although the useof heat to promote the setting will ordinarily be practiced in carryingout the present invention.

Another object is to avoid excessive penetration of the resin into theprinted surface, away from the pigment.

Other obiects and advantages of the invention will be evident as thedisclosure proceeds.

Inks prepared in accordance with the present invention are characterizedby having such formulation that the vehicle has the requisitecharacteristics for giving proper printing operations and also has suchratio of solvent to binder that adequately substantial modification ofthe solvent-binder ratio will cause such increase in the viscosity ofthe imprinted ink that it will be set sufliciently to be non-offsettingwhen subjected to the normal operations as referred to above. This muchvdesired result can be attained by so controlling the suspension balanceof the ink system that it will have the desired characteristics forproper printingsuch as tack, length, viscosity and press-stability, butthe solventbinder ratio is such that predetermined modification of thatratio will result, substantially instantaneously, in setting of theimprintedink to a condition of such non-tacky rigidity, i. e., acondition of such high viscosity or approximate solidity as to benon-offsetting against the operating conditions referred to. That is,the ratio of solvent to binder is within such range that while the inkwill handle quite satisfactorily in printing, the suspension balance ofthe ink system so approaches a critical solvent-binder ratio thatsubstantially decreasing the relative amount of solvent to binder willcause the imprinted film to set, as a solid 'or near-solid or gel; sothat it will withstand these operating effects of rollers, angle bars,folders and other instrumentalities in the press and also will benon-offsetting against ordinary handling pressures.

While printing inks of the general constituents to which this inventionrelates have been widely known and used for many years, so far as I amadvised there has been no clear and definite understanding of the natureof these ink systems and all the factors which control the setting ofthe inks after printing. Many efforts,

especially in more recent years, have been made to produce such inkshaving a solvent or liquid component which may be evaporated so as toleave the solvent freed binder and other constituents upon the paper, tospeed up the printing operations. But I have found that with properlyrelated constituents adequate setting may be caused by effecting apredetermined mod ification of the ink system balance, whether this iscaused by evaporation or otherwise. In such systems the ink may be soformulated as to be of satisfactory viscosity, and othercharacteristies, for good printing and the solvent-binder ratio, forproperly selected constituents, may be so close to a criticalrelationship that such substantial change in the system balance as willbe caused in approximately not more than one minute when the ink isimprinted on coated book paper will cause such very large increase inviscosity that the imprinted ink will set to a state which equals thatof a solid or near-solid, or gel.

While the type of critical viscosity range ink System is not fullyunderstood in all its aspects, the astonishing results from use thereofmay readily be seen and appraised.

This is true, whatever may be the entirely correct underlying theory. Inmy application Serial No. 346,801 filed July 22, 1940, now abandoned, ofwhich this present application is a continuation this phenomenon wasexplained in terms of preparation of a varnish in which the solvent-nonsolvent components are in such proportion that the solution orsuspension of the binder such as a resin chosen with respect to thevehicle, is almost at the point of precipitation upon the paper, thesolvent being diluted almost to gelation with the non-solvmt-i. e., to apredetermined state of incipient gelation. Such a system may be made soclose to the point of gelation, which would be a non-workably highviscosity, that a very small decrease of the controlling ratio--forexample, a variation in the 7 amount of solvent in the system-willresult in throwing the resin out of solution into a gel. This may beaccomplished in practical operations by adsorbing part of the solventinto the paper or its coating, ponents of the system may be so regulatedthat the ink gels or solidifies upon contact with the paper or likesurface which is printed with it. Or, by selecting a solvent which is oflower boiling range than the non-solvent diluent a minor loss of solventthrough evaporation, as by a suitable drying means, brings about anequally rapid gelling. By proper selection of materials such systems canbe made so critical that printing is impossible due to the disturbing ofthe critical balance during impression so that gelling occurs beforeplate and paper separate. Thus extreme nicety of control may beeffected. The terms solvent and "non-solvent herein are used forconvenience to distinguish respectively a relatively good solvent forthe binder, such for example as thermoplastic solid or semi-solid resinor modified resin material ordinarily used in heat set inks, and aninadequate solvent for such binder, which latter may be so inadequatewith respect to some particular resinous or hinder material as to besubstantially a non-solvent therefor. I am not certain that this theoryis correct insofar as it refers to the formation of a gelas that term,strictly speaking, may not properly apply to the very high viscosity setink impressions referred to. The set ink is of such greatly increasedviscosity that, as stated, it appears to be a solid or near-solid orlike a true gel; but whether it is a true gel or not, there is acritical range in the system balance such that a ratio of binder tosolvent in excess of the up per limit of such range, for the solventsand resinous binders possessing these related characteristics. willcause said great increase in viscosity to non-offsetting solidityregardless of whether it be a gel forming phenomenon or not. But, asthese ink systems will set even without evaporation of all the solvent,as heretofore considered necessary, and with quite substantial and theratio of the several comquantities of the solvent in the set ink itappears clear that the practicing of the invention does not involve thenecessity of forming a true gel, but that changing of the solvent tobinder ratio to reduce the relative amount of solvent will cause thesetting and this permits of making ink systems in which thesolvent-binder ratio may be so close to the critical value that settingmay be secured by removal of only a fraction of the solvent.

Whatever the theory, th gel or set ink as so formed will set or dry withor without added heat. Thus, when printed on paper in the usual manner,the inks of the present invention will ordinarily dry to non-offsettingcondition in less than one minute, at press or room temperature. Theusual inks now available require much longer to dry equally under likeconditions. On the other hand, if the printed impression made with inksof the present invention is subjected to added heat-e. g., to atemperature of about 200 C., which is used in common practice in dryinginks-the imprinted ink loses solvent, and hardens to dry, non-offsettingcondition more quickly than without the added heat. The difference inspeed of setting with and without added heat is much more marked,however, when printing upon completely non-absorbent materials, such asglassine, or metal foil. In such circumstances, the ink of the presentinvention dries so slowly at ordinary press temperatures or below thatadded heate. g. a temperature of 200 C. is required to efiect rapiddrying.

This invention permits of providing inks peculiarly adaptable andvaluable for high speed printing and an ink of such high speed thatsubstantially instantaneous setting may be attained. With the varnish ofthe ink in such state of potential or incipient gelation or setting, theink sets when the component ratio is varied beyond the criticalsolvent-binder ratio, as when brought into contact with paper or anylike more or less absorbent or adsorbent surface which causesdisturbance beyond the critical point.

When the system is one having a resinous material which is adequatelysoluble in a liquid consisting of a good solvent and a poor solvent forthe resin, then if the system is disturbed by removal of a minor butsuflicient fraction of the solvent component, as by evaporation, so thatthe critical gelation or non-solution point is passed, the ink will set.When this disturbance of the system occurs the formation of asubstantially solid material will start and proceed very rapidly, evensubstantially instantaneously. critical point in the system balance ofthis invention is passed and the ink is first set, it is at firstsomewhat soft and wet, but its viscosity is nevertheless so high as toequal that of a solid or gel, it goes quickly to such high viscosity andis a "near-solid despite the solvent remainin therein. It dries, in theabsence of added heat, by an action which may be somewhat analogous tosyneresis-that is, by exudation of some of the solvent as a result ofcontraction of the gel structore-and the solvent which thus separates islargely absorbed by the paper, whence it passes off by evaporation;although some of the solvent presumably evaporates directly into the airfrom the printed impression. The amount which evaporates in the lattermanner depends to some extent upon the ambient temperature. When heat issupplied, as is done in conventional heat-drying processes for settinginks, there is considerable evaporation of the solvent, following whichthe When the gel or resinous material sets to non-offsetting solidcondition due to cooling together with evaporation of solvent. This alsoexplains why drying of inks of the present invention without added heaton non-absorbent surfaces such as glassine and metal foil is so slowthesolvent which separates can not be taken up by the surface, to evaporatelater, and therefore remains in the impression, whence it evaporatesvery slowly at ordinary or press temperatures due to its low volatility.

Very satisfactory results are secured in producing inks according tothis invention by using resins and composite solvents such as thesolventnon solvent mixtures, chosen with proper respect to each other togive such potential gelation systems as described. In preparing thevarnish the resin and solvent are heated together sufliciently to meltthe resin and thereby to effect proper solution and homogeneity. Whenresins and solvent are heated together in this way, and then cooled,products of various characteristics ma be obtained. Thus, if the solventis an adequately good solvent for the resin, the cooled solution isstable. This is true whatever the constituents of the solvent material,some being much better sol- I vents for certain resins than others. Ifthe solvent-binder relationship is such that at the proper viscosity forprinting the ratio of solvent to binder is within the critical rangereferred to, then modifying the system balance as by removal of asubstantial amount of the solvent, to be outside the normal working orprinting range will give such remarkable and large increase in viscosityas stated and the printed impression will set, or gel or solidify to thenon-offsetting condition desired and described. It is to be understood,therefore, that whatever the theory, where a gel, or set, or solid ornear-solid condition is referred to herein, it refers to the settingwhich occurs as a result of such system balance modification.

Such solutions or suspensions of the resins usually available forcommercial use in inks, are in fact ordinarily colloidal solutions orsuspensions. The particle size of the suspension seems to vary with thesolvents and resins used and seemingly when poorer solvents, i. e.solvents of relatively low dispersing power, or more difficultydispersible resins, or both, are used, the particle size of the resin inthe varnish is larger, and the varnish becomes a colloidal suspension ofrelatively large particles. However that may be, by properly controLlingthe solvent and resin with respect to each other, and properly limitingthe excess of solvent over that which represents the critical solution,or gelation, point for the solvent and resin chosen a condit'on may beobtained where the solution is so close to the critical gelation pointthat variations in ratio which, practically, are so small as to beeasily attainable in commercial operations, may cause geiation orsetting to occur. Whether the particles separate as individual particlesor grouped together in aggregates, is immaterial. Individual particlesor an aggregate of particles are treated as a particle, since they areeffective essentially as one particle rather than as the individualcomponents. To meet only the requirements with respect to ratio ofsolvent to resin is not enough, however, as the combined properties ofthe system as varnish must be considered. Thus, a solvent may besatisfactory when used with some resins, but not with others.

The solvent should meet the following requlrements, with respect tovolatility, boiling range. and solvent power: It should be a relativelynon-volatile fluid at normal temperatures encountered in the press roomand in the fountain and printing unit, much less volatile than solventsheretofore commonly used. For exampie, I prefer to use a solvent which,when spread on filter paper in an amount of 400 mgm. on a 9 mm. circlewill lose not more than about 5% by weight in 20 hours standing at 25 C.in open, still air. Under like conditions, diethylene gly-' colmonobutyl ether, a typical solvent already known in the art, loses over30%. The initial boiling point should be high, and the boiling rangeshould be narrow so that clean evaporation can take place. Finally theliquid solvent used, such as the solvent-non solvent mixture referred toas particularly satisfactory should have the property of providing acritical narrow range or point so that by properly proportioning thesolvent and non-solvent to each other and to the resin the desiredapproach to the gelation balance of the system may be attained. Thedesired balance of such a system may be attained by mixing the solventand non-solvent in the proportions required, or by selecting acommercial material available or prepared to have the desiredsolvent-non solvent ratio, or the desired solvent action with respect tothe selected binder--i. e, to give the requisite printingcharacteristics and the critical range system balance. For example,resins commercially available at practicable prices are the alkyd andmodified alkyds which are substantially insoluble in paraflinhydrocarbons. Such resins however are soluble in aromatics such astoluol, and these compounds within the range from toluol to benzylbenzoate (boiling points varying roughly from about to 350 C.) may beused satisfactorily as the solvent portion of the system with a parafiinhydrocarbon such as kerosene as the non-solvent miscible component.Furthermore certain other compounds, such as some of the components(other than the paraifin hydrocarbons) which are found in commercialkerosenes are good solvents for various of the resins used in the inkindustry, and admixtures of these compounds, such as aromatics, ofproper boiling range and in proper ratio with lesser solvents for thetenacious resinous binders, such as the parafiin hydrocarbons, for usewith resins such as alkyd and modified alkyd resins as referred toabove, will provide a satisfactory varnish system.

The solvent-non solvent ratio and the proportion of solvent required maybe readily determined in the following manner-the resin is dissolved inthe solvent and non-solvent is then added until slight precipitationoccurs at which point sufficient solvent is added to redissolve theprecipitate and the refative proportions and ratio of the system thusdetermined. For example, the resin might be dissolved in toluol and aparafifin hydrocarbon such as kerosene substansystems having thecritical setting range may be formulated readily, as it permits ofdetermin ing the relative solvent-binder characteristics and by simpleadmixture and test permits of determining whether any such admixture ofcomponents is sufficiently close to the critical setting point whilealso of proper printing characteristics.

As an example a satisfactory ink of this invention may be made by makinga varnish consisting of Parts Resin 54.5 Rosin oil 43.0 Diamyl benzene2.5

Some resins on the market are satisfactory for use in making the inks ofthis invention and others are not. Resin manufacturers do not oftendisclose the precise character or method of manufacture of their roductsand therefore the suitability of the resin must be determined by actualtest, or exp'rience; or by testing the resin and if it is found toosoluble or not to provide the range of solvent-binder ratio or balancein the system with the solvent component desired to be used then bymodifying it and its characteristics, as by extending it as with linseedoil to give the desired solubility and solution balanc for the chosensolvent. The extending or modifving treatment will depend on the resinand the characteristics given to it when synthetically made by itsmanufacturer, but ordinarily for available and desirable mixtures suchas the solvent-nonsolvent ref erred to such synthetic resins as modifiedmaleic acid-glycerol alkyds will usually be heated with a drying oil,such as linseed oil, for periods varying from twenty minutes to threehours in proper proportion. For example in the varnish r'ferred to abovethe resin is an extended one prepared by heating 55 parts of a rosinmodified maleic-glycerol alkyd resin with 45 parts alkali refined gradelinseed oil at 580 F. for one hundred minutes, and then blended withgood solvent (di myl-benzene) and the poorer solvent at about 400 F. Thepoorer or non-solvent component in such example is an olefine andterpenefree rosin oil (the ordinary commercial rosin oil may haveincluded such constituents as to have too high solvent ower for thisresin). This procedure of extending resins with drying oils per mitsaccurate critical control of r sin solubility and tolerance in thesystem for the poorer or non-solvent component. Generally speaking thelonger the resin is cooked in the drying oil the less soluble itbecomes; but too much bodying in this manner produces an extended resinwhich will mottl in printing or will liver.

With such a varnish a satisfactory ink may be made by grinding in thepigment to the following formula,

Per cent Varnish 72.0 Carbon black 17.0 Blue toner 6.5 Milori bluepigment 4.0 Drier 0.5

In practice it has been found that a solvent such as thesolvent-non-solvent mixture above described meets the forzgoingrequirements, and that very satisfactory operating results are obtainedwhen such solvent has an initial boiling point of approximately 250 0.Furthermore cspecially satisfactory operating results have been attainedwhen the solvent components have such boiling rang-s that substantiallyall the oil boils within approximately a range of 10 C., or, at most, 15C. In determining the boiling range of high boiling oils, thetemperatures obtained depend to a considerable extent on the exactmethod of distillation. In the present process, the stated boilingranges w're obtained by using an 80 cc. sample of the oil in a 100 cc.standard Engler flask. The temperature was measured by a thermocouple inthe vapor instead of a thermometer, in order to avoid any temperaturecorrections. The rate of distillation was the same as in the ordinaryEngler. The apparatus, excepting the thermocouple, was the same as thatof the standard Engler.

It has been found also that a very satisfactory composite vehicle isobtainable commercially from Pennsylvania base oils refined to give afraction having a boiling range of 301-311 C., determined as abovedescribed. Such fraction has approximately 10% of non-paraffin compounds(understood to be aromatics) which have adequate solvent power foralkyd, modified alkyd, phenolic, etc. resins readily available fromvarious manufacturers, and this commercially produced admixture, ashereinafter described, has produced highly satisfactory commercial inksof this invention.

Properties required in the resin have been indicated above in describingthe solvent. By such determination it has been found that thePennsylvania base 301-311 C. boiling range kerosene fraction abovereferred to gives a thoroughly satisfactory commercial :nk which sets byseparation of the binder almost instantaneously where the solven tobinder ratio is decreased below a critical proportion. Such material isobtainable at commercally practicable prices, and also has itscomponents boiling within such a narrow ran e and at a temperaturesufiiciently low so that with the gas flame driers now used it readilyevaporates within the time allowed by present day high speed webperfecting presses and has good solvent release to give non-offsettingand fine printing effects. Resin mixtures may often be used toadvantage, in place of single resins.

Another satisfactory varnish may be made by using ethyl cellulose, forexample Per cent Ethyl cellulose 14.0 Benzyl alcohol 19.2 Dimethylphthalate 22.0 Mono amyl naphthalene 16.4 Benzyl benzoate 12.0 301-311mineral oil 16.4

With this varnish a satisfactory ink is Varnish 73.2 Carbon black 16.3Milori blue 10.5

' water.

lin, and bring the temperature of the mixture to between 50 and 55 C.This temperature is maintained for about -22 hours, during the first sixhours or so of which the stirring is continued. During this treatmentthe contents of the container assume a, golden red color. The caustic,which is used as a catalyst, is then neutralized by adding 95 parts ofHCl dissolved in 500 parts The .whole mixture is agitated and allowed tosettle; the lower layer, which is a sticky viscousliquid having a paleyellow color, is the phenolic-aldehyde condensate. This latter is drawnoff and washed with water. After separation from the water, the yield ofthe condensate is about 450 parts. This condensate is then reacted withmodifying agents in the following manner: 702 parts ester gum, 123 partsWW rosin, and 6 parts of lime-modified rosin, are uniformly meltedtogether and heated to 100 C. in an open container. To this mixture at100 C. is added 170 parts of the phenolic-aldehyde resin prepared asjust described, gradually and with stirring. The temperature is raisedslowly and by regular intervals, with some stirring. until after 6 hourselapses a temperature of 250 C. is reached. The reaction is thenstopped, and the product is cooled and ready for use. The yield is about850 parts.

The resin so prepared will be referred to herein as resin R, and hassuch characteris ics that when admixed with solvent, as herein set out,it will give an ink component having a system falling within thesolvent-binder range specified and having those characteristics whichprovide the superior inks of this invention.

A satisfactory varnish for use in accordance with the present inventionmay be prepared by mixing -45 parts of such resin R and 60-55 parts ofthe 301-311 mineral oil (parts being by weight) in the presence of heatas described hereinafter. A varnish which is even better with respect toprinting qualities may be prepared by incorporation of a small amount ofester gum, for example, in the proportions by weight of 33.3 parts resinR, 16.7 parts ester gum, and parts of the 301-311 mineral oil.

Other properties of both solvent and resin can be best set forth by adescription of the properties of the varnish.

Referring, for example to the varnish comprising the 301311 mineral oil,the varnish of the present invention has the property when standin; inbulk, at room temperature, that the varnish remains free of gel or solidfor at least 24 hoursexcept that some varnishes close to the criticalsetting or gelation point may exhibit a purely superficial skin orpellicle of gel on surfaces exposed to the air or the container.

Also the viscosity of such varnish is relatively high. The desiredviscosity for use in the present invention may be obtained by properadmixing solvents and resins having the proper characteristics relativeto each other. As the viscosity varies with the temperature and thetemperature I may vary materially because of room temperaturevariations, and also because the temperature of the ink in the fountainespecially in high speed presses, increases very materially over thefirst few hours of operation the viscosities at these temperaturesencountered are important considerations. In commercial inks of thisinvention using the 301-311 C. petroleum fraction satisfactory varnisheshave been made, as follows,

Varnish A.Equal parts resin R and 301-311 mineral oil.

1'2 Varnish B.-Equal parts Dammar gum and 301-311 mineral oil.

Viscosity in centipoises :\l,

Varnish A is just below the critical gelation or setting point at 27 C.;however, if the percent of solvent is slightly increased, to not overthe viscosity drops sharply to the general range of that of varnish B.For most printing purposes, the viscosity of varnish A at 27 C. is toohigh, and .it is preferable to increase the amount of solvent to bringthe viscosity down to the general range of that of varnish B. Of ifdesired, the viscosity can'be reduced by maintaining the varnish and theresulting ink at temperatures somewhat above 27 C.e. g. at about 35 C.For most operations the viscosity of the varnish and the resulting inkshould be between about 1100 and 6000 centipoises at 27 C., althoughhigher viscosities may be suitable in some instances. varnishes havingviscosities below 1100 centipoises at 27 C. are to be avoided, however,as being too thin for suitable general use. In the commercial inksreferred to the preferred varnishes specified above should, whencomposed of equal parts by Weight of solvent and resin, have viscositiesat least equal to that shown for varnishes composed of equal parts ofDammar gum and 301-311 mineral oili. e. at least equal to about 2750centipoises at 27 C. and under such characteristics will give unusualresults of quick setting, fine printing and drying into fine qualityprinted product.

Inasmuch as slight changes in the procedure for preparing the resin, orof incorporating the resin with the solvent (as well as changes inresin-to-solvent ratio, and in temperature) affect the viscosity, it isevident that exact duplication of the results shown is not necessarilyalways possible, but that nevertheless these are fairly representativeof varnishes of the types to which each pertains. And, as stated above,by using resin R and a solvent component having the characteristics ofthe 30l-31l C. material as described a vehicle is obtained which servesadmirably as a yardstick by which to measure other resinous-solventsystems and also the completed inks made from a vehicle of thisinvention within the critical solvent-binder ratio and having theviscosity, and other desirable ink characteristics, which make for goodprinting and also having the system balance suificiently close to thecritical value so that the quick setting will occur upon modification ofthat balance as described.

It is evident from the above, and from trial in operation, that theillustrative varnishes of the present invention are very much nearer tothe critical gel state than are common prior art varnishes. Also it isevident that a new and novel criterion for the coordinated selection ofa commercially available admixture of the so-called solvent-non solvent,or other available solvent component, and suitable resin therefor isprovided. Certain Texas base petroleum fractions, for example, ifprepared to have the same 301- 311 C. boiling range would neverthelessact quite difierently from the Pennsylvania base fraction describedabove and would require quite different processing and treatment tosecure the inks and the results attainable with this invention. For suchTexas base fraction has a much larger ratio of solvent to non-solventand therefore is not comparable to a solvent exemplified by the 301-31lC. referred to above and would not produce the system balance, orcondition of potential or incipient gelation to be near the criticalSetting or gelation balance above described. But by the method ofdetermination above described the critical system balance or settingpoint and the required solvent-binder ratio and the utility of thefraction for the practicing of the present invention may be readilydetermined.

The above will serve to illustrate some of the points already discussedwith respect to the fact that inks made in accordance with the presentinvention, in spite of their relatively low Volatility, uponmodification of the system balance will change over so rapidly from ,thecommercially good printing viscosity to such greatly increased viscosityas to set to such a solid or near-solid or gel condition that they willbe non-offsetting. even though substantial quantity of the solventcomponent remains in the imprinted ink. Referring to the illustrativevarnish A described above, the small described increase in the solventto binder ratio thereof will decrease the viscosity from just short ofsettin to about 2750 centi poises at 27 C. It is thus evident that acorresponding decrease in solvent to hinder ratio of the imprinted ink,as by withdrawal into the paper, will cause an equally harp increase inviscosity from said satisfactory printable viscosity to a viscosity sohigh that the imprinted ink will set into the very high viscosity whichattends the solid or near-solid or gel condition. Thi same decrease mayreadily be caused by evaporating a part of the solvent, substantiallyinstantaneously, in the heat setting printing processes referred to andas some solvent also will penetrate into the paper, the ink will set tothe non-offsetting very high viscosity condition instantaneously, orsubstantially instantaneously. Such inks have the suitable and desirableviscosity characteristics for good printing, and also have thecharacteristics of the solvent and binder with respect to each otherthat with such printable viscosity the system balance is such thatvarying the solventbinder ratio as described will cause the system topass the critical ratio above which the viscosity increases so sharplythat the ink changes from the comparatively low printing viscosity, tosuch a greatly and sharply increased viscosity that the ink acts, orsets, as a solid or near-solid or gel condition. Other solvent andbinder constituents may be admixed having the same order of viscositycharacteristics in the same solvent-ratio range to give the desiredprintin and also, after printing, to give like great increase to theviscosity of a solid, or near-solid or gel by like decrease in thesolvent to binder ratio. It has been found that when such binder-solventinks are made so that there is a sufficiently sharp increase inviscosity with increase in ratio of binder to solvent they will set withextreme rapid ty to the very high viscosity non-offsetting conditiondescribed. And by means of this invention such inks ma be made up ofmaterials so selected that within the easily attained solvent-binderrange of ratios referred to the desired high quality printing may beeffected and the rapid setting then caused. Two inks may be formulatedof differing materials such that both have the same ciently set andfluent and tacky and therefore unsatisfactory. For example, two testswere made on commercial black inks both for use in high speed, heat set,letter press printing of an illustrated magazine. One of them was madeof solvent and binder materials having such relative qualities as togive the system balance and solvent-binder ratios within the range ofthis invention and the other outside thereof. The first upon removal ofsolvent to bring the binder content to about 80% had its viscosityincreased to about 213x10 poises, while upon removal of the same amountof solvent from the other the viscosity was found to be 9.5 10 poisesand was found insufficiently dry to be satisfactory while the former setto the desired solid. near-solid or gel condition. This decrease inratio of solvent to binder is about that which occurs with solvents ofthe character herein referred to while passing through heat dryingequipment now commercially used on letter press magazine printing, andapproximates in result that slight decrease in solvent from the ratio ofsolvent to 50% binder described above which is caused in approximatelyone minute at a temperature of 27 C. by imprinting the ink on a coatedbook paper. As will be evident the increased setting viscosity of theink of this invention is tremendously greater than with the ink whichwas formulated to be outside the solventbinder ratio range of theinvention.

It is clear that inks typical of the present invention are much lessvolatile at any given temperature than are the usual prior art inks,represented by the other illustration. While the varnishes of thepresent invention at press temperatures (about 50 C.) and above arefluid enough to be used in ordinary high speed printing operationswithout difiiculty; yet a relatively slight drop in temperature of evena few degrees centigrade causes imprinted films to become exceedinglyviscous.

In preparing varnishes in accordance with the present invention, I mixtogether the resin or resins and the solvent both selected in accordancewith the requirements already set forth, at a temperature of say 250-290C., until the mixture is homogeneous. This temperature should be abovethe melting point of the resin and below the boiling point of thesolvent. After the resulting varnish has cooled, pigments are added asdesired and the mixture is intimately ground in a conventional ink millor other apparatus. The amount of solvent used is generally equal to orslightly more than the amount of resin, by weight.

Several suitable resins and mixtures of resins have already beenreferred to herein, including resin R, a mixture of resin R and estergum.

' Dammar gum may be used, but this gives a varnish which is about on theborderline of satisfactory workin conditions. It will be noted thatwhile the viscosity of a varnish made from equal parts Dammar gum andthe 301-311 C. mineral oil is within the preferred range neverthelesssuch a varnish is insufficiently near the point of incipient gelation atabout 27 C. to be suitable in this present invention as are varnishessuch as those represented by the satisfactory examples above. A Dammergum varnish can, however, be

' 15 improved by the addition of a small proportion of rosin. Othernatural or synthetic resins, and mixtures of them, may also be used,including mixtures of ester gum and phenolated copal resins, andmixtures of rosin with cumar or alkyd resins.

Pigments are ground into the varnish just described in the same mannerand in approximately the same proportions as in the ordinary printingink practice.

After the ink is thus prepared, it is used in printing in the usualmanner. Inasmuch as this ink is relatively non-volatile, the precautionsnow frequently necessary to prevent volatilization and resultant settingor caking of ink on the printing press mechanisms, and otherdisadvantages which result from upsetting of the solvent-to-resin (orthe varnish) ratio, need not be observed.

Conventional drying procedure, wherein the printed impression ".1subjected to a temperature suflicient to melt the resin (e. g. 200 C.)is ad- I vantageous, but not always necessary.

It should be observed that the ink ofthe present invention does notrequire additional agents such as plasticizers and other specialmaterials commonly added in inks hitherto available. For example, highboiling solvents or plasticizers such as dialkyl phthalates, tricresylphosphate, and blown or heat bodied oils such as castor, linseed, andtung have been incorporated with resins and solvents for the resin inpreparing varnishes. One of the principal reasons for these additionshas been to assist in retaining fluidity of the inks after the almostinevitable loss of some of the relatively volatile solvent prior tomaking the printed impression. In the preferred practice of theinvention, the use of these addition agents is unnecessary. It isthought this may be due to the retention of some solvent in the set inkafter the drying operation is completed, which solvent is thought to bein suflicient amount to prevent undue brittleness of the printed inkfilm even though the extremely sudden and sharp increase in viscosityhas caused the ink to set to a viscosity condition practicallyapproximating a solid or gel. It should be noted that While the 301-311C fraction referred to herein has been used in large scale commercialoperations in the inks of this invention, it is not an essentialconstituent as other solvent components may be used so long as they areof such character as to be press stable, to give a good printable ink,and to give a system balance such that the great viscosity change willoccur upon the modification of the system balance.

While the foregoing disclosure describes in detail the preferredembodiment of this invention and some modifications thereof, it will beunderstood that this disclosure is for the purpose of illustration onlyand that various changes may be made without departing from the spiritand scope of the invention as set forth in the appended claims.

What is claimed is:

1. A printing ink comprisin as essential ingredients an organic liquidcarrier which is substantially non-volatile at normal press roomtemperatures, a linseed-oil-extended rosin-modified maleic glycerolalkyd resinous binder and a pigment, said liquid carrier consisting of amixture of a paraffin hydrocarbon liquid which is a non-solvent for saidresinous binder together with an aromatic hydrocarbon liquid which is atleast as volatile as said parafiin hydrocarbon liquid, is miscible withsaid parafiin hydrocarbon liquid carrier varnish having a viscositywithin the range of 1100-6000 centipoises at 27 C., said cal paraflinhydrocarbon liquid comprising at least the major proportion of saidliquid carrier.

2. A printing ink comprising as essential ingredients an organic liquidcarrier, a linseed oilextended rosin-modified maleic glycerol alkydresinous binder and a pigment, said liquid carrier consisting of amixture of paraffin hydrocarbon liquid which distills within the rangeof 301-311 0., and which is a non-solvent for said resinous bindertogether with an aromatic hydrocarbon liquid which distills within therange of 301-311 C., which is miscible with said paraflin hydrocarbonliquid and which is itself a solvent for said resinous binder, theamount of said liquid carrier being within the range of 50-60 per centof the total of said liquid carrier plus said resinous binder and theamount of said aromatic hydrocarbon liquid being sufiicient to maintainsaid resinous binder in solution and to provide a liquid carrierresinous binder varnish having a viscosity within the range of 1100-6000centipoises at 27 C., said paraflin hydrocarbon liquid comprisin atleast the major proportion of said liquid carrier.

3. A printing ink comprising as essential ingredients an organic liquidcarrier, a linseed oilextended rosin-modified maleic glycerol alkydresinous binder and a pigment, said liquid carrier consisting of amixture of paraflin hydrocarbon liquid which distills within the rangeof 301-311 C., and which is a non-solvent for the resinous binder,together with an aromatic hydrocarbon liquid which distills within therange of 301-311 (3., is miscible with said parafiin hydrocarbon liquidand which is itself a solvent for said resinous hinder, the amount ofsaid liquid carrier being within the range of 50-60% of the total ofsaid liquid carrier plus said resinous binder, and the amount of saidaromatic hydrocarbon being approximately 10% of said liquid carier, theliquid carrier plus resinous binder providing a varnish having aviscosity within the gange of approximately 1100-6000 centipoises atJOSEPH G. CURADO.

REFERENCES CITED The following references are of record in the file ofthis patent:

OTHER REFERENCES Industrial and Engineering Chemistry, vol. 35, No. 10,October 1943, page 1044.

1. A PRINTING INK COMPRISING AS ESSENTIAL INGREDIENTS AN ORGANIC LIQUIDCARRIER WHICH IS SUBSTANTIALLY NON-VOLATILE AT NORMAL PRESS ROOMTEMPERATURES, A LINSEED-OIL-EXTENTED ROSIN-MODIFIED MALEIC GLYCEROLALKYD RESINOUS BINDER AND A PIGMENT, SAID LIQUID CARRIER CONSISTING OF AMIXTURE OF A PARAFFIN HYDROCARBON LIQUID WHICH IS A NON-SOLVENT FOR SAIDRESINOUS BINDER AND A WITH AN AROMATIC HYDROCARBON LIQUID WHICH IS ATLEAST AS VOLATILE AS SAID PARAFFIN HYDROCARBON LIQUID, IS MISCIBLE WITHSAID PARAFFIN HYDROCARBON LIQUID AND WHICH IS ITSELF A SOLVENT FOR SAIDRESINOUS BINDER, THE AMOUNT OF SAID LIQUID CARRIER BEING WITHIN THERANGE OF 50-60 PER CENT OF THE TOTAL OF SAID LIQUID CARRIER PLUS SAIDRESINOUS BINDER AND THE AMOUNT OF SAID AROMATIC HYDROCARBON BEINGSUFFICIENT TO MAINTAIN SAID RESINOUS BINDER IN SOLUTION AND TO PROVIDE ARESINOUS BINDERLIQUID CARRIER VARNISH HAVING A VISCOSITY WITHIN THERANGE OF 1100-6000 CENTIPOISES AT 27* C., SAID PARAFFIN HYDROCARBONLIQUID COMPRISING AT LEAST THE MAJOR PROPORATION OF SAID LIQUID CARRIER.